1982 CB750F...Better Devil

Maritime

Well-Known Member
then again the next one down was this:
https://www.ebay.com/itm/Mini-Universal-Motorcycle-Mechanical-12K-RPM-Tach-Tachometer-Gauge-1-4/151666316926?epid=1537126653&hash=item235004567e:g:iZgAAOSws0pcFjL4

fits CB750 and is 1:4 and I am not sure if it's correct or not.
 

Jimbonaut

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irk miller said:
When the two CB750's that I currently own and the other that I did own changes from 4:1 to 1:4, I'll let you know. ;)
Ha! I'm not doubting you Irk, I'm just confused by what I reading. The tach that Dime City sells for CB750's is listed as 1:4 (as are a lot on eBay etc). And this dude selling the Triumph repro tach tells me his is a 4:1 and therefore won't work with my bike. It just all got a bit confusing and by a bit I mean a whole shitload.
 

Nybz

Member
4:1 for all stock CB750 DOHC or SOHC ....don’t know where the 1:4 came from, typo probably.
You are all good


Sent from my iPhone using DO THE TON
 

pidjones

Well-Known Member
I still contend that on an engine that can spin to 10k, no one is going to design a tach that requires the tach cable to spin at 40,000 RPM.
 

Jimbonaut

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CrabsAndCylinders said:
What Pj says would seem to make sense.
Concur wholeheartedly. Think I've explained by now where the confusion stems from however, so I'm going to do everyone a favour and never say the words tach or ratio ever again in the same sentence.

Might not say them individually either. Bollocks to both of them ;D
 

cxman

Active Member
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"I still contend that on an engine that can spin to 10k, no one is going to design a tach that requires the tach cable to spin at 40,000 RPM."

what could go wrong????
 

Jimbonaut

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Entry-level question - bearing in mind that I'l be cramming whichever engine part will fit into my very small shop oven to cure the paint, is there a particular kind of masking tape I should use to stand up to the heat or would regular painter's tape do the job?
 

doc_rot

Oh the usual... I bowl, I drive around...
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i just peel off the masking tape before I bake. there is also high temp powder coating tape.
 

adventurco

Nick Ol' Eye
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The Jimbonaut said:
D'oh. Remove it before baking! I scare myself sometimes.
I always try to pull tape when the paint is still pretty fresh, too. Usually whenever the can says "dries to the touch". I've seen some paints (rattle can) that like to chip if you pull the tape after its cured for a day. But that also could have been caused other factors.

Who knows? But that's how I do it anyways.
 

Jimbonaut

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Removing the tape before baking is absolutely what I'll do. Just feel a bit daft asking a question with such an obvious answer. Still, no such thing as a silly question - something I have to remind myself when I have a d'oh moment :eek:
 

Maritime

Well-Known Member
advCo said:
I always try to pull tape when the paint is still pretty fresh, too. Usually whenever the can says "dries to the touch". I've seen some paints (rattle can) that like to chip if you pull the tape after its cured for a day. But that also could have been caused other factors.

Who knows? But that's how I do it anyways.
+ one or even a little sooner, nothing worse than pulling tape and having an edge flake off a nice clean job.
 

Jimbonaut

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After a closer look at the mating surfaces on the cylinder block and head, it's clear that they're going to need a bit of a hone to clean them up a bit. Plan is to tape some sandpaper onto the granite countertop in the kitchen (before or after the missus cooks her breakfast - all bets are off. If this is my last post, she wasn't happy), lower the mating surface onto it and give it a clean.

What would be the best grade sandpaper to use? I'm thinking 1000 grit?
 

Jimbonaut

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Finished up the fins on the head -



Filed them to get a flat profile (cheers for the tip Maritime), sanded them (400, 600, 1000 then 2000) and then polished (red compound ("tripoli"), then white compound ("diamond") then Autosol). Came up aces.
 

Maritime

Well-Known Member
Nice. And I cant take credit. I read to file somewhere on the vastness of the interwebs LOL. Just passed it on after trying it.
 

Jimbonaut

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Well, yesterday was mating surfaces day. Turns out, you never see mating surfaces day coming. One minute you're in front of the telly watching footie with a mate, the next you're taping sand paper to the kitchen countertops. Mating surfaces day. You never see it coming.

I ended up using 240 grit first, then 400. Asked Mrs K if she was cool with me bringing half my engine into the kitchen and having at it with a couple sheets of sandpaper, and when I say asked I mean didn't ask. Taped up the paper like so -



and lowered the cylinder block onto it. For the first time since remodelling the kitchen I found myself agreeing with my wife that there wasn't enough counterspace (I didn't know what the hell she was talking about - now I do) - really could've used another sheet in there for more of a "slide". No matter, it's all good. Here's what it looked like before -



and here's the after -



Not perfect (couldn't shift those couple of darker areas) but a load better. Pretty sure I can live with it.

The head was a bit trickier - the exhaust studs stuck out a little too far and meant I'd fuck up the granite in double quick time. Had a re-think, dug out a collage my lovely and highly arty wife made for me years ago and taped some paper to that instead -



- the thick glass made it perfect for getting into the hard to reach places and kept a uniform flat surface. Don't have a before an after of the head but it came up good too. Hauled everything back into the garage, got out a stanley and cleaned up the gasket from the cylinder block -



Surfaces...mated. Ready for mating anyway.
 

irk miller

You've been mostly-dead all day.
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Just curious, but did you check the true on that countertop? Curious how close it is to a proper surface plate. Most surface plates are several inches thick to accommodate flex from the surface it sits on, as well as being ground to within .0000025"
 

Jimbonaut

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Also dug out the large o-rings that sit in the recesses around each cylinder underneath the block. They were no longer rubber - snapped like plastic as I pried them out. 35 years will do that to an o-ring.

Thanks to a care package that arrived last week (cheers Maritime) I now have my repro Triumph bars, stainless engine bolts, valve cover bolt seals and powdercoat samples. Really threw a curveball at myself when deciding about a colour for the frame, but wanted to try something a little different. The tank is going to be a green gold, and I think I'm going with this for the frame -

. https://www.youtube.com/watch?v=Wtmktb7uSoI

It's pretty much black, but looks gold in some angles. Could work, one way to find out.
 

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